1. Field of the Invention
The present invention relates to an image capturing apparatus having a distance measurement function for measuring a distance of an object and capturing an image of the object, and more particularly an image capturing apparatus for measuring a distance to the object so as to detect whether the object exists in an image capturing range.
2. Description of the Related Art
An image capturing apparatus for capturing an image in a predetermined range of an object by irradiating the object with uniform light is widely used. In an image processing system using an image captured by such the image capturing apparatus, a sharp image is particularly required.
For example, with the development of biometric technologies in recent years, there have been provided a variety of apparatuses for personal identification by which an individual can be distinguished by capturing an image of a living body by which an individual can be distinguished and recognizing a feature of the living body, for example, fingerprints of limbs, eye retinas, face and blood vessels.
In particular, blood vessels and skin patterns of a palm and a finger are suitable for reliable personal authentication, because a relatively large amount of personal feature data may be obtained therefrom. Further, it is believed that the patterns of blood vessels (veins) do not change from the time of an embryo throughout the lifetime of any person, and that no identical pattern exists among any persons without exception, which are therefore suitable for personal authentication. FIGS. 19 through 22 show explanation diagrams of the conventional blood vessel image authentication technique. As shown in FIG. 19, at the time of registration or authentication, a user puts a palm of a hand 110 close to an image capturing apparatus 100. The image capturing apparatus 100 emits an ear infrared ray, and irradiates it the palm of the hand 110. The image capturing apparatus 100 receives the near infrared ray reflected from the palm of hand 110 by a sensor.
As shown in FIG. 20, hemoglobin in the red corpuscle flowing in a vein loses oxygen. Such the hemoglobin (deoxidized hemoglobin) absorbs the near infrared of the vicinity of 760 nm in wavelength. Accordingly, when the palm is irradiated with the near infrared, reflection is reduced in a portion in which a vein exists. Thus, by the degree of strength of the reflected near infrared, the location of veins can be recognized.
As shown in FIG. 19, first, the user registers a vein image data of the own palm into a server or a card, using the image capturing apparatus 100 shown in FIG. 19. Next, to perform personal authentication, the user makes the vein image data of the own palm to be read, using the image capturing apparatus 100 shown in FIG. 19.
The personal authentication is performed by collating the registered vein image, which is extracted using a user ID, with a vein pattern in the collation vein image being read above. For example, in the case of the collation of the vein patterns between the registered image and the collation image as shown in FIG. 21, the person is authenticated as genuine. Meanwhile, in the case of the collation of the vein patterns between the registered image and the collation image as shown in FIG. 22, the person is not authenticated as genuine (see Japanese Unexamined Patent Publication No. 2004-062826, FIGS. 2-9).
For such the biometric authentication or the like, it is necessary to capture an image of an object (a portion of a human body in case of the biometric authentication) in a non-contact manner. For this purpose, the image capturing apparatus 100 emits light producing uniform light intensity in a certain image capturing range (distance and area), receives the reflected light of the above image capturing range by a sensor, and outputs a captured image signal as an electric signal.
FIGS. 23 and 24 show explanation diagrams of the conventional image capturing apparatus. As shown in FIGS. 23 and 24, the image capturing apparatus 100 includes an image capturing unit 120 at the center, and in the periphery thereof, a plurality of light-emitting devices 130-1 to 130-8. The dotted lines shown in FIG. 23 represent the range of the light having uniform intensity emitted from an individual light-emitting device among the plurality of light-emitting devices 130-1 to 130-8.
As such, by disposing a plurality of (here, eight) point light sources in the periphery of image capturing unit 120, the image capturing range of the image capturing unit 120 can be irradiated with the light of uniform intensity. Meanwhile, image capturing unit 120 includes a photoelectric conversion unit 122 such as a CMOS sensor, and an optical system 124 such as a lens. Since the photoelectric conversion device 122, which is a plane photodetector device, has a predetermined light receiving area, a predetermined optical distance is required to guide the reflected light of the image capturing range onto the light-receiving plane of the photoelectric conversion device 122. For this purpose, a lens 124 such as a fish eye lens is disposed between the photoelectric conversion unit 122 and the object, so that an image of the predetermined image capturing range is projected onto the light-receiving plane of photoelectric conversion device 122.
Thus, conventionally, in order to irradiate the object with each point light source element 130-1 to 130-8 by sharing a predetermined image capturing range, the point light source elements 130-1 to 130-8 have been disposed apart from each other, as shown in FIG. 23. Also, in order to supply the light of predetermined uniform intensity to the image capturing range, the point light source elements 130-1 to 130-8 have been disposed nearer to the object than the photoelectric conversion device 122, as shown in FIG. 24 (see WO 2004/088588, FIGS. 1 and 6).
Further, in such the image capturing apparatus, it is necessary to detect whether the object is positioned at a focal distance. Conventionally, an optical distance sensor having a light emission portion and a light reception portion has been provided in the image capturing apparatus, so as to measure the distance to the object (see WO 2004/088979, FIGS. 1 and 5). For example, the optical distance sensor has been provided between the point light source 130-4 and the image capturing unit 120 shown in FIG. 24.
In the above conventional image capturing apparatus, the distance sensor includes the light emission portion and the light reception portion. Since the distance is measured from the position of the reflected light, it has been necessary to dispose the light reception portion apart from the light emission portion. This causes the sensor of interest to become a large size. Also, miniaturization of the image capturing apparatus has been difficult and there has been a restriction when incorporating the image capturing apparatus into equipment.
Also, in order to detect the inclination of the object also, it is necessary to mount a plurality of distance sensors, which further causes difficulty in miniaturizing the image capturing apparatus with restriction to incorporate into equipment, and impediment to cost reduction.